Incandescent lamp.



H. NEEDHAM. INCANDESCENT LAMP.

APPLICATION HLED OCT- 2. I912.

Patented June 20, 1916.

Inventor: Harry H. Tleedham,

itness es His fittorneg.

UNITED STATES PATENT OFFICE.

.LARRY H. NEEDHAM, OF EAST ORANGE, JERSEY,

ASSIGNOB TO GENERAL nnnc'rmc comrm, a conrommon or NEW YORK.

mcmnscnnr To all whom it may concem:

Be it known that I, HARRY H. NEEDHAM, a citizen of the United States, residing at East Orange, county of Essex, State of New Jersey, have invented certain new and useful Improvements in Incandescent Lamps, of which the following is a specification.

My invention relates to incandescent lamps, especially those having metallic filaments, and its object is to produce an improved incandescent lamp. To this end I prolong the useful life of the lamp and improve its candle power performance.

My improved lamp may .be exhausted in the same manner and by the same methods as the incandescent lamps heretofore used, consequently such a good vacuum is obtained that arcing and similar defects due to imperfect exhaustion or poor vacuum are avoided. The lamp may be and preferably is so made that the bulb remains practically clear during useful life of the lamp.

In accordance with my invention I introduce into the lamp bulb some suitable substance which produces the desired results during the normal running of the lamp Without spoiling either the vacuum or the appearanceof the lamp. The lamp may be exhausted in the usual manner and may be heated during exhaustion to the high temperature necessary to drive out occluded gases and water vapor and to produce a good vacuum without any deleterious effects being produced in either the vacuum or the lamp by the substance in the lamp bulb. The substance in the lamp bulb has such a low vapor pressure that it does not spoil the vacuum when heated during exhaustion or during the normal operation of the lamp. It is preferably anhydrous and non-hygroscopic, to avoid the introduction of water vapor into the bulb, and should be of such a character that it does not spatter orcause de posits on the lamp bulb. The substance which"- I prefer to use is a fluorid or double fluorid which is more stable when heated than sodium chlorid and evolves when heated to tempera tures above 400 C. and to higher temperatures conveniently attainable in the lamp, as for example, 800 0., a chemically active atmosphere at a pressure which does not exceed that of a first class vacuum, as, for example, cryolite, which is a double fluorid of sodium and aluminum. The substance or compound may be placed anywhere inthe Specification of Letters Patent.

lamp as long as its temperature when the lamp is lighted is between certain definite limits where the pressure of the chemically active atmosphere produced by it does not exceed that of a first class vacuum and its beneficial eflect is marked.

For a better understanding of my invention reference may be had to the accompanying drawings which show, merely for purposes of illustration, some of the various forms in which my invention may be embodied in an incandescent lamp.

Figure 1 is a view of a lamp with the substance secured to the lower filament support; Fig. 2 is a View of a similar: form of lamp with the substance secured to the top support; Fig.3 is a View of a similar form of lamp with the substance mounted on a special wire or support; and Fig.4 is a view of a different form of lamp with the substance mounted on a special support.

The substance or compound which I prefer to use is cryolite, a mineral composed of a double fiuorid of sodium and aluminum. This mineral is put into the lamp in any suitable way, preferably by grinding it to a very fine powder, passing the powder through a silk bolting cloth, and then making the powder into a paste which is applied to some suitable part of the lamp. The powder may be made into a paste with any suitable binder, or even with water. I prefer to use the binding material used in making the carbon paste commonly used to cement carbon filaments to the leading in wires of carbon filament lamps. Very little binding material is necessary, and it may be either inorganic, such as a solution of Waterglass, or organic, such as caramel solution, glucose,'a gum, or tarsolution.

The'paste'is applied to the lamp in any convenient way. The preferred method of applying it is illustrated in the drawings. In Fig. 1, for example, the lamp has a mount comprising a glass rod 1 provided with upper supports 2 and lower supports 3 for holding the metallic filament 4. The outer ends of the supports are shaped into hooks 5 for holding the filament. Before the mount is placed in osition in the bulb the aste is applied to t e lower supports 3 in t e form. of a bead or mass 6 which does not touch the filament. To guard against detachment of the bead 6 from the support in case of rough usage the bead should en- Patented June 20, 1916. Application filed. October 2, 1918. Serial No. 723,500.

gage both wires of the hook. As shown in Fig. 2, the bead 6 can be placed on the upper supports 2 as well as on the lower supports 3. It can also, as shown in Fig. 3, be placed on a special support or wire 7 secured to the glass rod 1 to hold the bead 6 in roper thermal relationto the filament 4.. n the form of lamp shown in Fig. 4 the bead 6 1s placed on a. special wire or support 8 which is carried by the stem of the lamp and which holds the bead in proper relation to the filament 9, owing to the ease with which the powdered material mixed with a binder can be placed in any desired relation to the filament to bring the material to the proper temperature when the filament is incandesproper temperature when the lamp is lighted, and in many types of lamps a receptacle cannot be so placed without spoiling the appearance or distribution of light of the lamp. A mixture of cryolite and binding material, is very inconspicuous and can be secured to any part of the lamp mount, especially when made in the form of a bead 6.

After the paste is applied to the mount the paste is dried and then heated or baked to remove gases and water vapor and carbonize the binding material. The paste may be heated by a small pointed flame to just a visible temperature, or the whole mount may be placed in an oven and baked at 300 deg. C. Overheating of the paste does not affect the action of the cryolite, but may remove so much of the carbon of the binder that the beads are weakened and may drop off if the lamps are subjected to rough handling. After the paste has been heated or baked the mount is ready to be put into the then ready to be exhausted.

A lamp embodying my invention and containing cryolite or asimilar substance can be exhausted by any of the standard methods of exhausting lamps of the usual type and can be heated as hot as necessary while being exhausted. A lamp which is not heated above 250 deg. C. during the exhaust operation is liable to give 0 gas and moisture from the glass when the lamp is lighted. It is desirable to heat the lamps to between 360 deg. 375 deg. C. while. exhausting them, and this can be done with lamps embodying my invention, as the melting point of cryolite is about 1050 deg. C. and its vapor pressure is low not exceeding that of a first class vacuum even at temperatures as high as 800 C. As cryolite is not at all hygroscopic it does not introduce moisture into the bulb, and lamps contaming it give no trouble by arcing from these causes.

The cryolite can be placed anywhere 1n the lamp as long as it attains a temperature of between 300 deg. C. and about 700 deg. or 800 deg.'C. when the lamp is lighted and is in normal operation. Between these temperatures the cryolite is most active and gives the best results. As a result of the wide range of temperature over which the cryolite exerts its beneficial action there is no necessity for careful adjustment and regulation of the conditions under which the lamp runs, as the beneficial efl'ect of the cryolite'will be obtained under all ordinary conditions. I prefer to mount the cryolite in such a position in the lamp that when the lamp is lighted the cryolite will have a temperature of about 500 deg. C. When so mounted it will not spoil the vacuum as its vapor pressure is very low, being substantially that of a first class vacuum. Another advantage is that it does not spatter, and it causes practically no discoloration of the bulb. A lamp containing cryolite has throughout its useful life a vacuum so good that it is classified as a first class vacuum by the customary coil test, and there is no trouble from arcing.

While I do not wish to advance any theory as to how the cryolite acts, it seems probable that at the proper temperature the cryolite produces in a lamp a certain halogenous atmosphere which is chemically active and of the proper pressure, and that there is some dissociation of the cryolite. If this halogenous atmosphere impairs the vacuum the impairment is so slight that it cannot be detected as the vacuum is rated as a first class Vacuum by the usual coil test and there is no trouble from arcing or other difficulties due to poor vacuum.

Although at present I consider cryolite the preferable substance to use in carrying out my invention, it will be understood that any other fluorid or double fluorid which is at least as stableas sodium chlorid when heated and which evolves an atmosphere chemically active to tungsten at a pressure not exceeding that of a first class vacuum at temperatures attained by these substances when exposedin the lamp in convenient locations may be used instead of cryolite. For example, the cryolite may be mixed with other fluorids of greater stability than sodialkali and of some other base, as, for example, FeF 2KF. All such substitutions and modifications I consider to be within my invention.

What I claim as new and desire to secure by Letters Patent of the United States is 1. A tungsten filament incandescent lamp containing a solid fluorid which at temperatures below 400 C. is substantially inactive but at temperatures exceeding 400 C. evolves an atmosphere chemically active to the material of the filament to hinder ob-w scuration of the bulb and at a pressure not 7 adjacent to the filament to attain when the filament is incandescent a temperature over 400C. and to maintain said atmosphere in the lamp at a pressure not exceeding that of a first class vacuum. I

3. A tungsten filament'incandescent lamp containing a powdered non-hygroscopic fluorid at least aS stable as sodium chlorid when heated and evolving when heated above 450 C. an atmosphere chemically active to tungsten to hinder obscuration of the bulb and at a pressure not exceeding that of a first class vacuum, said fluorid being-secured by binding material adjacent the heated above 450 C. when the filament is mcandescent to evolve throughout the life of the lamp said atmosphere at a pressure not exceeding that of a first class vacuum. 4. An incandescent lamp having a tungsten filament and containing a double fluorid of an alkali and ofanother base which is at leastas stable as sodium chlorid'when heated and evolves at temperatures above 450 C. an atmosphere chemically active to tungsten to hinder obscuration of the bulb but is substantially inactive-5' below 450 C., and at a and evolving and maintaining said atmosphere at a pressure not exceeding that of a 'rst class vacuum while the lamp is lighted.

5. An incandescent lamp containing a' double fluorid of sodium and aluminum.

6. An incandescent lamp containing cryolite positioned in the lamp to attain dur ng ament and normal operation of the lamp a temperature between 300 deg. C. and 800 deg. C.

7. An incandescent lamp containing cryo-- lite mounted in thermal relation to the filament to attain a temperature of about 500 deg. C. during normal running of the lamp.

8. An incandescent lamp comprising a filament, a support for said filament,- and a bead of cryolite paste on the filament support in position to attain during normal operation ofthe lamp a temperature between about 400 C. and 800 C.

9. A tungsten filament incandescent lamp containing a mass composed of a binder and a non-hygroscopic solid fluorid compound at least as stable as sodium chlorid when heated and positioned in said lamp adjacent the filament to attainduring normal operation of the lamp a temperature of about 500 C. and evolving at said temperature an atmosphere chemlcally active to the material of the filament to hinder obscuration of the bulb and at a pressure not exceeding that of a'first class vacuum.

10. A tungsten filament incandescent lamp containing a mass of powderedfluorid at least as stable as sodium chlorid when heated and secured to the mount of the lamp by means of binding material adjacent the filament to attain while the lamp is lighted a temperature from 400 C. to 800 C. and activated over said temperature range to an atmosphet'e chemically active to the metal of the filament and at a pressure not exceeding that of a first class vacuum. to hinder blackening of the lamps.

11. A tungsten filament incandescent lamp containing a mass of solid decomposable fluorid at least as stable as sodium chlorid when heated and having a vapor tensionnot exceeding the pressure of a first class vacuum at temperatures from 400 C.-to 800 C. and mixed with binding material to form a head on a filament supporting wire adjacent the filament and attaining when the lamp is lighted a temperature over. 400 C. and

maintaining in the ulamps an atmosphere chemically active. to tungsten to hinder ohscuration of the bulb and at a pressure not I exceeding that of a'first class vacuum.

my hand this thirtieth day of September, 1912.-

Witnesses: v

I J. H. Enxms, 1 S.-N. W.

HARRY'H. NEEDHAM.

In witness whereof; I have hereunto set 3110 

